The fourth century was a time when Christianity’s deepest questions were being debated and clarified: Was Jesus fully God and fully man or fully God and partially man—or vice versa? Were the Father and the Son one being or two similar beings? What about the Holy Spirit—was he also God? If so, how could there be only one God? The nature of the Trinity was as mysterious then as it is now, and only the best-trained philosophical minds could hope to offer the ancient world a coherent understanding of the Father, Son, and Holy Spirit.